Unit 7 - Ozone

• What is Light?


  - visible ... is part of the electromagnetic spectrum

  - visible ... is 400nm-700nm

  - a wave and all of the waves travel at the same speed (the speed of light)
• Wave Length


  - the distance from peak to peak of each wave

  - shorter ... = GREATER ENERGY

  - longer ... = LOW ENERGY

  - ... and energy are inversely related
• The Electromagnetic Spectrum (from high energy light waves to low)

  - Gamma Rays (short wavelengths, close together, HIGH ENERGY)

  - X-Rays

  - Ultra-Violet (comes from the Sun)

  - Infrared (visible light)

  - Radio Waves (long wavelengths, far apart, LOW ENERGY)
• What 3 Things Can Happen When Light Hits Matter?

  1. It can reflect off - mirror

  2. It can pass through - window

  3. It can be absorbed - energy is transferred

  - Different wavelengths of light react differently to different things
• Infrared Light


  associated wit the greenhouse effect, global warming and climate change
• Ultra Violet Light


  associated with the production of Ozone and the hole in the Ozone
• What 3 things have been pumping O2 into the atmosphere for 3+ billion years?

  1. Plants

  2. Algae

  3. Photosynthetic Bacteria
• 3 Types of UV Light

  1. UVA 320-400nm

  2. UVB 280-320nm

  3. UVC < 280nm
• Oxygen and UV Light

  UVC + O2 -> 2O

  - occurs 30-50 KM above Earth

  O + O2 -> O3

  - produces ozone
• Measure Ozone in Dobson Units

  if you remove all gases except the ozone and compress them to 1 atmosphere, the atmosphere would be 3mm thick

  - Equal to 300 DU
• The Hole


  Sept. 1984 "suddenly and unexpectedly" the ozone had dropped by 50% and returned 6 weeks later

  - Ozone Hole (October 2018)
• Sherwood Rowland


  a chemist with an interest in the atmosphere who did work on CFC's

  - Chlorofluorocarbons - invented by DuPont in 1930 for refrigeration (freon-11)
• Sherwood Rowland's Experiment


  Shined UV to a glass box...

  UV Light -> O3 -> O3

  UV Light -> CFC -> NO CFC

  UV Light -> O3 and CFC -> NONE OF THE 2

  - revealed CFC's have a damaging effect on the ozone in the atmosphere so by 1970 they were banned from all "non essential use"
• How does the Hole in the Ozone Work?

  Multi-Step Process (4 steps)

  1. Because CFC's are inert, they can travel to the upper atmosphere

  2. In the upper atmosphere, CFC's are photolysised (split by sunlight) and produce HCL and CLONO2

  - HCL and CLONO2 don't damage the ozone but drift around the atmosphere
• How does the Hole in the Ozone Work? pt.2

  it is in Antarctica because they have...

  3. Polar Stratospheric Clouds catalyze HCl + CIONO2 -> Cl2 + HNO3

  4. UV Light returns and Cl2 is photolyzed into CIO.

  - A CLO can remove 1000+ molecules of ozone